A method for manually stipulating the ratio of a continuously variable transmission (hereinafter, xe2x80x9cCVTxe2x80x9d).
The operational strategy of a CVT is first normally to allow comfortable driving and second to achieve a favorable consumption of fuel. As for good drivability, essential criteria lie in a proper relation between the speed of rotation (hereinafter, xe2x80x9cRPMxe2x80x9d) of the motor and the speed, in the motor dynamics, and in meeting such vehicle performance as is desired by a driver. Additionally, consideration must be given to adaption to the circumstances of travel, i.e., to city or mountain driving. Also, reliable downshifting into the highest ratio (LOW) upon stopping must be considered. Further, intervention by the driver during shifting must be easily carried out. For a satisfactory fuel consumption, what is to be striven for, is an extended period of operation in the most efficient zone of the characteristic curve of the motor, as well as a lowering of the RPM of the motor during a period when travel conditions are constant. Since the named criteria for operational strategy of a CVT are, in part, self contradictory, a compromise is normally struck.
In order to combine the advantages of a continuous change of the transmission ratio, with known gear change behavior and the motor acoustics of an automatic staged gear change transmission associated therewith, U.S Pat. No. 4,836,056 proposes to automatically switch the operational strategy of the CVT over to a control, which is based on a shifting-characteristic curve. This switchover is effected automatically, dependent upon a threshold signal representing the motor load. The achieved gear change behavior of the CVT can, in this case, be likened to an automated gear change with a very soft torque converter in which a converter bypass clutch is always open up to a particular throttle flap threshold. The RPM behavior of the motor can be regarded negatively by the driver, described as producing a xe2x80x9cseat of the pantsxe2x80x9d effect or xe2x80x9crubber band effectxe2x80x9d.
In order to bring the operational behavior of the CVT to automatically coincide better with the desires of the driver and the influences of the travel conditions, adaptive driving strategies have become known.
For instance, DE-OS 43 12 415 proposes to adjust the ratio by means of more than one type of characteristic curve of the motor map. In doing this, the operational point direction is carried out in an area between a characteristic curve of optimal fuel consumption and a characteristic curve of optimal motor loading. The operational points, between these limiting lines, lie on so-called dynamic characteristic curves, the position of which is dependent on the magnitude of the speed of change of the load demand. The choice of the shift-characteristics and the current dynamic characteristic curve, along which the operational point is directed, is done automatically.
DE-PS 41 20 546 describes an operational strategy for a CVT wherein there is a control characteristic curve according to which the continuous ratio selfadjusts in relation to the position of the throttle valve flap and the RPM of the motor. The said control line, however, represents the driving style, that is, the driving activity of the driver. The data for this xe2x80x9cstylexe2x80x9d characteristic curve, however, is automatically selected from a multiplicity of control characteristic curves previously stored in the memory of the transmission control. The evaluation of the driver""s style, that is the driving activity, is a complex function and the cost in time and money in ifs application is correspondingly great.
In DE-OS 196 00 915, the applicant describes a procedure for the guidance of an operating point, in an operational mode in which the actual preselected position of the operational point, is in a state of being continually newly determined within a predetermined zone of driving with an upper and a lower limit activated by the function of an actual, essentially drive-dependent, unfiltered input signal. Based on this, the location of the operational point in the transmission variogram is continually being computed anew and predominately defined by the activities of the driver in this case.
In all procedures for automatic operational point guidance, the disadvantage is that, in spite of the applications of great efforts, not all the desires of the driver can be fulfilled, in particular, a desire to be able to make a manual intervention during shifting.
To offset this particular disadvantage, DE-PS 41 20 540 proposes that along with a first operational mode of automatic driving strategy, a second is to be created in which the driver, by means of manual intervention, can simulate the operational behavior of a multistage transmission. For this situation, a number of set, constant ratios, i.e. shift movements, for example, are input and stored in a characteristic map. If the driver gives a manual shift command to the transmission, then the choice of the constant transmission ratio is generated from the said characteristic map relative to a driving activity. Upon the transition from the first operational mode into the second manual operational mode, by means of a selection-apparatus which is manipulated by the driver, a transition function controls the jump of the actual transmission ratio, which is running at the moment of change of operational mode, onto the next successive, constant, predetermined ratio. In order to better represent the desires of the driver during the manual type of shifting operation, DE-PS 41 20 540 proposes further to select the gear change jump out of groups of predetermined constant ratios, which simulate different characteristics of shifting, for example, a fuel consumption optimized, an economic ratio and a load optimizing, sport characteristic.
In the case of the simulation of a stage transmission with constant ratios as a manual operational strategy for a CVT, the disadvantage lies especially in the diminishing of drivability in the functional area of the operational map. In this way, the motor can be throttled down in the lower speed zone by a ratio which is so low that the motor stalls which, for a normal automatic driver, would present surprising behavior for the vehicle. Also, the available power for start would be surprisingly low if the driver had negligently forgotten to shift down through all gears upon stopping. Because of the customary spread advantage of the continuous transmission, during a start-up situation, the driver must change the gears very quickly, in the lower speed areas, in order to achieve an optimum acceleration. As a solution for this problem, DE-PS 41 20 540 proposes a forced high shifting or a forced up-shifting in fixed, predetermined gear changes, this being triggered when threshold speeds are reached.
EP 0 697 548 A1 describes a driving strategy for a CVT, in which, for a second operational mode, discrete, manually preselective, vectors are provided, which all intersect at a virtual zero-point. This virtual zero-point lies outside of the variogram of the CVT in the negative vehicle speed area and the positive motor RPM area. This, then, makes it impossible in all manual, preset vectors to achieve the start-up ratio LOW and the maximum vehicle speed.
Thus, the invention has the purpose of creating a method for stipulating the ratio of a CVT with a first, automatic operational mode and a second, manual operational mode in which the driver has direct intervention in the choice of ratio and wherein there will be an improvement in the operational behavior in the manual operational mode.
The purpose of the invention is achieved in that the driver, in the manual operational mode of the CVT, can manually predetermine, by means of a shift or selector apparatus, the RPM of the motor which is dependent upon a non-staged, vehicle velocity.
In accord with the invention, it is proposed, to so simulate the manually selectable curve of the RPM of the motor as an optional curve profile within the adjustability area of the transmission variogram, that with each RPM curve, both the start-up ratio (LOW) and the highest speed of the vehicle can be achieved.
The predetermined motor RPM curves are processed within the electrohydraulic control of the CVT and/or processed in accord with regulation/control technology and issued as predetermined ratios to the variator. The invented, manually selectable, motor RPMs can be expressed also as vehicle speed-dependent variator input RPMs or as variator ratio curves. The carry-over function between the motor RPM and the variator input RPM is then to be correspondingly considered, by a torque converter as a start-up element between motor and variator for instance, as a converter characteristic curve.
As to the invention, there lies on the one hand, the subjective sensitivity of the driver in the judgement of the connection of the motor RPM and the driving load. On the other hand are the technical presuppositions of the CVT, considering the adjustability area of ratio change as well as the possibilities for guidance of the operational point.
Besides the driving noise associated with the speed, the acoustic sensitivity of the driver orients itself on the RPM of the motor. This is particularly true for the manual operational mode of the transmission operation in which the driver knowledgeably intervenes in the operational point guidance of the motor. In this case, the invented method presents advantages through the direct driver engendered stipulation of motor RPM curves.
Normally, CVTs, in comparison to automatic stage transmissions, have an advantage in spread. The total spread is designedly incorporated into the LOW (largest ratio) and the overdrive (OD) (smallest ratio). Usually, the start-up ratio LOW of a CVT is less than the ratio of the first stage of an automatic, staged transmission.
This has the result that the motor, at a full load start-up and with transmission ratio in the LOW region, runs up to the maximum RPM more quickly.
If, in the manual operational mode of the CVT, the transmission ratio is maintained as a specified shift position as, for example, is described in DE-PS 41 20 540, then the driver must make his shift very quickly in order to obtain an optimum mesh with the next gear position. Since, in accord with the purpose as achieved by the invention, the driver can manually shift into a continuous curve of motor RPM, then the likewise continuous transmission tracks the ratio, in an advantageous way, with help from the predetermined RPM curve and follows with a continuous, forced, up shift. Accordingly, the vehicle reacts without a break in the delivered load, and remains unchanged with an optimum increase in speed, without the necessity that the driver once again must manually intervene.
Conditioned by the large total spread, the highest ratio, i.e. OD, of a CVT is normally greater than that of the greatest stage of an automatic stage transmission. It is possible in the manual operational mode of the CVT in the overdrive ratio, to drive at very low rotational speeds, and therewith, travel at very low rotational speeds for the motor. The critical part here is bringing the vehicle to a stop from such an operational point, especially in connection with a strong braking effort. In order to achieve sufficient drive loading, in the case of a subsequent start-up, the transmission must remain unchanged in the manual operational mode and be shifted in the direction of the start-up ratio. If, in the manual operational mode of the CVT, the transmission ratio is constantly constrained in set gear stages, then the driver, must shift individually through all stages, in the time remaining before stand still, in order to once again drive in LOW.
The situation in regard to coming to a stop out of OD becomes more difficult for the driver in the manual operating mode, because of being accustomed to the comfort of the stopping in the first operational mode with continuous, automatic ratio changing.
The invented manual specification-input by the driver of the RPM of the motor solves the problem in a simple and elegant manner. Conditioned by the optional formulation of the manually selectable RPM curve, the ratio, especially dependent on the speed of the vehicle, makes the transition without stages, as a continuous forced down-shift from the OD-ratio into the LOW-ratio, without necessitating intervention by the driver.
The method, in accordance with the invention, blends together the advantages of the possibilities of driver instigated manual intervention in the operational point guidance of the motor-transmission-unit and the comfort and security of a continuous RPM behavior of the motor by means of a CVT.
Further essential advantages of the invention arise through the integration found in the control of the ratio or RPM of the non-stage transmission. The transition between the speed of rotation curves which are individually, manually selectable are freely formulated. xe2x80x9cSoftxe2x80x9d shifts, based on need, lead to a noticeable relief of the RPM control or ratio regulation of the variator and improvement of the driving comfort similar in effect to the continuously forced up-shift, in the direction of the greatest speed, and the continuously forced down-shift, in the direction of vehicle stand still. The application output is relatively small. Moreover, special functions, which in the first automatic operational modes of the CVT are available, can be easily integrated into the second manual operational mode.
In a development of the invention, the proposal is made to integrate a start-up element, placed between the drive motor and the variator, in the manual operational strategy. In this way, the operational zonexe2x80x94now limited between the mechanical marginal ratios LOW and OD of the variatorxe2x80x94can be extended as long as the start-up element is not fully closed. In the case of a hydrodynamic torque converter with an integrated converter override clutch (WK), the additional hydraulic adjustable area in an open WK is defined by the converter characteristic. In the case of a clutch, the lower limit of the adjustment range is defined by the clutch slip characteristic, as long as the clutch is not completely closed.
In another development of the invention, the proposal is that the manual operational mode of the continuous transmission, because of superimposed input signals, be immediately abandoned and a transition made into the automatic operational mode and, upon the deletion of the superimposed input signal, a return is once again made into the manual operational mode. This back-and-forth switch is not detectable by the driver. Superimposing input signals are, for instance, a kick-down shift command (KD) of the driver, or a message from the anti-blocking system xe2x80x9cABS-Activexe2x80x9d. In this way, important special functions, which are effective in the automatic operational mode of the CVT, may be mutually incorporated into the manual operational mode in a simple manner.
In the second manual operational mode of the CVT, the driver chooses preselected, curves of the RPM of the motor, by means of a shift lever, which are related to the ratio positioning of the transmission. In the case of a shift command for a change in the RPM curve, the actual RPM curve is transferred by means of a control function to the new RPM curve, starting from the actual operational point, whereby the transition function can be in the form of an optional curve.
In one embodiment the proposal, in keeping with the invention, is to so formulate the transition function that the motor RPM transition, i.e. the variator input RPM or the ratio transition, be computed as a function of the position of the actual operational point, relative to the targeted RPM or relative to the start-up RPM curve. In particular, the proposal is made to control or regulate the motor RPM gradient, between the two motor RPM curves, by means of the ratio of the difference of actual motor RPM and that RPM of the vehicle-speed-corresponding target RPM curve to the vehicle-speed-corresponding difference-RPM between the start-up RPM curve and the target RPM curve.
In an advantageous manner, a xe2x80x9croundxe2x80x9d RPM transition improves the shifting comfort. This is valid for similar transitions, for instance a change to a high RPM level, such as in a down-shift, as well as motor RPM transitions which are like in form and again similar to ratio transitions. Moreover, round RPM transitions relieve the necessary safety functions of the variator adjustment against undesirable variator slippage.
In the case of a change of the automatic operational mode of the continuous transmission into a manual operational mode, accomplished by the driver by means of a shift or selection apparatus, DE-PS 41 20 540 proposes to first retain the actual transmission ratio. A jump is made to the next neighboring constant ratio, only in the case of a further shifting command of the driver. The amount of the first shift-jump, in an unfavorable case, can be a half or a one-and-a-half of a regular stage shift.
Counter to this, in the invention the proposal is made, in the case of a change from the automatic to the manual operational mode, to retain the RPM, that is, the ratio in accord with the position of the actual operational point, the position being primarily relative to the upper and lower successive predetermined motor RPM curves or variator input RPM curves or yet the ratio curves. In an advantageous manner, a harmonious driving behavior is formed immediately after the operational mode change by the tracking of the RPM, that is, the ratio relative to the non-equidistant curves. Upon the next manual shifting command, the tracking operational point transitions over to the next adjacent RPM curve or ratio curve.
In another embodiment of the operational mode change, in accord with the invention, the proposal is made at first retaining the actual ratio or the actual motor RPM or the actual variator input RPM. If the operational point which, in this way, is only tracking as far as vehicle speed, strikes upon the next preset RPM curve or ratio curve then, henceforth, the operational point will be guided to track along the characteristic curve to the next manual shift command. In an advantageous manner, the operational point will be automatically conducted to a manually selectable RPM characteristic curve, that is, the adjustment characteristic curve.
In a further embodiment of the change of operational mode, it is proposed that directly upon the change from the automatic to the manual operational mode, a change is made to the next higher situated motor RPM curve. In an advantageous manner, this operational mode change strategy gives consideration to the fact that the driver leaves the automatic operational mode directed to the target in order to directly acquire a higher motor capacity or achieve manually an even higher degree of motor brake effect.